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    <h3>Implementation Repository</h3>
    <P> In the previous example, the client must contact the server
      at least once. If the server has been moved to a different host or
      port, or if the server is down, binding between the client and
      the server fails. Indirect binding through an external location
      broker like the Implementation Repository solves this problem.
    </P>
    <P>An implementation repository maintains a data structure known
      as a server table to keep track of the servers. It maintains a
      registry of known servers, records which server is currently
      running on which host and at which port number, and starts
      servers on demand if they are registered to do so.
    </P>
    <P> When a server
      creates a persistent reference, it sets the address and port
      number in the profile body of the IOR to point at the
      implementation repository that is responsible for the server.
      When a client uses this IOR, it gets connected to the
      implementation repository, provided the implementation
      repository is not down. The repository decodes this IOR and uses
      the POA name from the object key to index into its server
      table. The repository replies with the current addressing
      information of the actual server. The client now sends the
      request to the actual server.
    </P>
    <P>In this example, let's proceed to modify our previous stock
      factory example to support indirect binding through an
      implementation repository.
    </P>
    <P>The only thing we have to do for this is to register our
      childPOA with the implementation repository.
    </P>
    <PRE>
       orb->_tao_add_to_IOR_table ("childPOA", stock_factory.in ());
    </PRE>
    <P> Then, we stringify all the object references as usual and
      print them out.
    </P>
    <PRE>
       CORBA::String_var ior = orb->object_to_string (stock_factory.in ());
    </PRE>
    <H3>Exercise</H3>
    Modify the <a href=../Server/server.cpp>server.cpp</a> in the simple
    server to  create the persistent child POA.
    You can use the same
    <a href=../Quoter.idl>Quoter.idl</a>
    <a href=../Server/Stock_i.h>Stock_i.h</a>
    <a href=../Server/Stock_i.cpp>Stock_i.cpp</a>
    <a href=../Server/Stock_Factory_i.h>Stock_Factory_i.h</a>
    <a href=../Server/Stock_Factory_i.cpp>Stock_Factory_i.cpp</a>
    <a href=../Client/client.cpp>Client.cpp</a>
    You can use this <a href=Quoter_Simple_Impl_Repo_Server.mpc>MPC file</a>.
    <H3>Solution</H3>
    Compare your server.cpp with <a href = server.cpp>server.cpp</a> file.

    <H3>Testing</H3>
    <P>To test your changes, you need to run four programs. The first
      step is to start up the Implementation Repository provided
      with TAO. The Implementation Repository is split into one locator at least
      one activator. The locator provides the interface visible
      to the application intending to use the repository (in our case,
      the client), while the activators do the real work of activating
      and maintaining servers.
    </P>

    <P>First, we start the locator. We need to dump the IOR of the ImplRepo_Service to a file,
      so that both the activator and the client can find the locator.
    </P>
    <PRE>
       $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator -o implrepo.ior -d 0 -ORBobjrefstyle URL &
    </PRE>

    <P>Second, we start the activator, pointing it to the locator's IOR file.
    </P>
    <PRE>
       $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_activator -ORBInitRef ImplRepoService=file://implrepo.ior

          ImR Activator: Starting doc.ece.uci.edu
          ImR Activator: Registered with ImR.
    </PRE>

    <P> Next, we need to register our server with the implementation
      repository. We can use the
      <CODE>$TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator</CODE>
      application provided with TAO to add our server to the server
      database in the implementation repository.
    </P>
    <PRE>
       $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator -ORBInitRef
         ImplRepoService=file://implrepo.ior add childPOA -c
         "./server -ORBUseIMR 1 -ORBobjrefstyle URL -ORBInitRef
         ImplRepoService=file://implrepo.ior"

          Successfully registered server <childPOA>
    </PRE>
    <p> On Windows platforms, use this command instead to register the server
      in the implementation repository
    </p>
    <PRE>
    $ACE_ROOT/bin/tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior
    add childPOA -c "./server -ORBUseIMR 1 -ORBobjrefstyle URL
    -ORBInitRef ImplRepoService=file://implrepo.ior"
    </PRE>
    <P> We specify the <CODE>-ORBInitRef</CODE> option to use the IOR in
      the <CODE>implrepo.ior</CODE> file and the <CODE>-ORBUseIMR</CODE>
      option to tell the server to use the IMR for notification of its
      startup and shutdown.
    </P>
    <P>The next step is to generate a simple IOR for our server
      to be used with the IMR, using the
      <CODE>ior</CODE> option, and write it to <CODE>stock_factory.ior</CODE>.

    </P>
    <PRE>
       $tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior ior
       childPOA -f stock_factory.ior

         corbaloc:iiop:1.1@doc.ece.uci.edu:2690/childPOA
    </PRE>
    <P> From now, the implementation repository is all set to keep
      track of our server and do the needful on a method invocation
      on our server.
    </P>
    <P> Now, execute the client as usual.
    </P>
    <PRE>
       ./client file://stock_factory.ior MSFT RHAT

       The price of a stock in "Microsoft, Inc." is $91
       The price of a stock in "RedHat, Inc." is $210
    </PRE>
    <P> For testing the persistency of the POA, let's shut down the
      server and then run the client.
    </P>
    <PRE>
       $tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior
       shutdown childPOA

         Successfully shutdown server <childPOA>

       ./client file://stock_factory.ior MSFT RHAT

         The price of a stock in "RedHat, Inc." is $210
         The price of a stock in "Microsoft, Inc." is $91
    </PRE>
    <H3>More Reading</H3>
    <P>More information on Implementation Repository is
     <A  HREF="../../../../../docs/implrepo/index.html">here</A>.
    </P>
      <P>The <A HREF="http://www.triodia.com/staff/michi-henning.html">Henning</A> and <A HREF="http://www.iona.com/hyplan/vinoski/">Vinoski</A>
      <A HREF="http://www.iona.com/hyplan/vinoski/#book">CORBA book</A> discusses POA policies in detail.  Likewise,
      the Schmidt and Vinoski
      <A HREF="http://www.cs.wustl.edu/~schmidt/report-doc.html">columns</A> in C++ Report also include several articles about the POA.  Finally,
      the <A HREF="http://www.dre.vanderbilt.edu/~schmidt/TAO.html">TAO</A>
      distribution includes <A HREF="../../../../../examples/POA">examples</A> that illustrate how
      to use the POA policies.
    </P>
    <hr>
    <address><a href="mailto:pgontla@ece.uci.edu">Priyanka Gontla</a></address>
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Last modified: Sat May 19 17:19:07 CDT 2001
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